1. Field
This disclosure relates generally to semiconductor devices, and more specifically, to packaged semiconductor devices with lead frames.
2. Related Art
Some types of packaged semiconductor devices include an integrated circuit die mounted on a lead frame. Lead frames are commonly manufactured by stamping/punching preformed sheets of metal such as copper, copper alloys, and iron-nickel alloys into desired shapes. Lead frames may also be made by etching the preformed sheets. Lead frames may also be made by plating metal in a desired pattern onto a carrier that is subsequently removed.
The lead frame includes conductive leads that extend from close proximity to the die to beyond the outer edges of the package body. Wire bonds are formed between the die and the lead frame to form a die assembly that connects the die to bond pads on the lead frame. The die assembly is then placed in a mold that encases the die and the wire bonds or other electrical attachments. Mold compound is inserted or injected into the mold. Mold encapsulant is formed around the die and the wire bonds to protect the die and wire bonds from corrosion, water, and external forces that may damage the die or break the wire bonds.
The ends of the leads that extend outside of the encapsulant are bent so that a foot portion of the lead can be soldered to contacts on a substrate such as a printed circuit board. In some situations, the assembly is subjected to wide variations in temperature, which causes the substrate to expand and contract at rates that are different than the encapsulated die assembly, placing stress on the bonds between the leads and the substrate. It is therefore desirable to provide assemblies that can operate is in wide temperature ranges without breaking contact between one or more of the leads and a corresponding contact on the substrate.